Modeling the liquid–gas interface using self-assembled monolayers

Stochastic classical trajectory simulations were used to study the efficiency of the energy exchange at the gas–liquid interface. Self-assembled monolayers (SAM) of long-chain functionalized molecules were used to mimic the liquid surface. Since the molecules in the monolayers are anchored by only one end, they retain some of the mobility that they have in the liquid but lose all their fluidity. The corrugation of the surface and the stiffness of the interface were tuned by varying the length of the molecules in the monolayers. The use of longer molecules leads to increased corrugation of the surface and provides additional dissipation channels that promote more efficient momentum and energy accommodation, increase the translational–rotational energy interconversion and enhance trapping. However, this “length effect” appears to saturate, as no further significant changes are observed in those properties when the monolayerʹs moleculesʹs length is elongated from six to nine carbons. This saturation effect suggests that, even though monolayers can provide some of the mobility observed in liquid surfaces, they lack the energy dissipation channel provided by the fluidity of the liquid.